Method and apparatus for allocating a plurality of data symbols in a wireless communication system

ABSTRACT

A method of allocating a plurality of data symbols from a transmitting end using multiple carrier modulation (MCM) is disclosed. More specifically, the method includes receiving the plurality of data symbols from a serial-to-parallel converter, grouping the plurality data symbols into at least one data symbol group, wherein the at least one data symbol group is formed by grouping a specified number of neighboring data symbols, and allocating the at least one data symbol group to at least one subcarrier group, wherein the at least one subcarrier group is formed by grouping a plurality of subcarriers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational App. No. PCT/KR2006/002253 filed on Jun. 13, 2006, whichclaims the benefit of earlier filing date and right of priority toKorean App. No. 10-2005-0051558 filed Jun. 15, 2005.

TECHNICAL FIELD

The present invention relates to a method and apparatus for allocatingdata symbols, and more particularly, to a method and apparatus forallocating a plurality of data symbols in a wireless communicationsystem. Although the present invention is suitable for a wide scope ofapplications, it is particularly suitable for more efficientlyallocating the data symbols.

BACKGROUND ART

An Orthogonal Frequency Division Multiplexing (OFDM) scheme or anOrthogonal Frequency Division Multiple Access (OFDMA) scheme is used fortransmitting high speed data in wired and/or wireless channels. Theseschemes are actively being researched. In the OFDM scheme, frequencyusage efficiency increases since this scheme employs a plurality ofsubcarriers having mutual orthogonality. In the transmitting end and thereceiving end, a process of modulating and demodulating the plurality ofsubcarriers are similar to performing an Inverse Discrete FourierTransform (IDFT) and a Discrete Fourier Transform (DFT), respectively.As such, an Inverse Fast Fourier Transform (IFFT) and Fast FourierTransform (FFT) are used to achieve high speed data communication.

The principle of OFDM scheme includes dividing a high speed data streaminto a plurality of low speed data streams which are then transmittedvia the plurality of subcarriers. By using the subcarriers to transmitthe plurality of low speed data streams, symbol duration is increasedwhich in turn works to reduce relative dispersion in a time domain basedon multi-path delay spread. In the OFDM scheme, the data is transmittedin units of transmission symbols.

In an OFDMA physical (PHY) layer, active carriers are divided intogroups, and each group is transmitted to different receiving ends. Thesegroups of carriers are referred to as sub-channels. Each sub-channelcomprised of carriers can be close in proximity with each other orspaced equally apart from each other. By permitting multi-access persub-channel, although transmission of the carriers becomes more complex,frequency diversity gain, gain based on focusing the power, andefficient execution of omni-directional power control can be attained.

FIG. 1 illustrates a block diagram of transmitting/receiving ends usingan OFDMA scheme in an uplink direction. First, a data stream is mappedusing a modulation technique (e.g., Quadrature Phase Shift Keying, 16Quadrature Amplitude Modulation) and then is converted into Nu number ofparallel data using serial-to-parallel conversion. From total of Ncnumber of subcarriers, these symbols are mapped to Nu number ofsubcarriers while remaining subcarriers (Nc-Nu) are padded (e.g., zeropadding). Thereafter, Nc-point IFFT is performed to the symbols.

In order to reduce inter-symbol interference, a cyclic prefix is addedto the symbols and then transmitted after the symbols are convertedusing parallel-to-serial conversion. The operation of the receiving endis the same process of that of the transmitting end except in reverseorder. A different user's data can be transmitted using an availablesubcarrier from unused subcarriers (e.g., Nc-Nu).

FIGS. 2 a-2 c illustrate methods of mapping Nu number of subcarriers outof Nc total number of subcarriers. FIG. 2 a illustrates a randomallocation of subcarriers, FIG. 2 b illustrates allocating thesubcarriers by collecting the subcarriers in specified frequency bands,and FIG. 2 c illustrates allocating each subcarrier throughout theentire frequency bands in equal intervals.

Since the mapping methods illustrated in FIGS. 2 a-2 c make use of theentire frequency bands, frequency diversity can be achieved. However,because each subcarrier is allocated individually, timingsynchronization of OFDM symbol of different users can be off, and signalquality can suffer due to nearby subcarriers of different users ifDoppler frequency is large. Furthermore, in the conventional OFDMAscheme, a single user uses a plurality of subcarriers and as a result,poor Peak-to-Average Power Ratio (PAPR) characteristics can appear andan expensive power amplifier is needed to resolve the poor PAPR problem.

In order to alleviate the poor PAPR characteristics, a DFT spread OFDMAscheme has been proposed. The DFT spread OFDMA scheme is a data symbolprecoding method using DFT matrix. FIG. 3 is a block diagramillustrating transmitting/receiving ends using a DFT spread OFDMAscheme.

The difference between the DFT spread OFDMA scheme and the conventionalOFDMA scheme is that in the DFT spread OFDMA, Nu number of data symbolsare Nu-point DFTed. Thereafter, as illustrated in FIG. 2 c, theconverted data symbols are mapped in equal intervals to the entire Ncnumber of subcarriers. In addition, although the PAPR can be drasticallyimproved by using the DFT spread OFDMA, the function of the DFT spreadOFDMA easily heats up due to an Inter Channel Interference (ICI).

DISCLOSURE OF THE INVENTION

Accordingly, the present invention is directed to a method and apparatusfor allocating data symbols in a wireless communication system thatsubstantially obviates one or more problems due to limitations anddisadvantages of the related art.

An object of the present invention is to provide a method of allocatinga plurality of data symbols from a transmitting end of using multiplecarrier modulation (MCM).

Another object of the present invention is to provide an apparatus forallocating a plurality of data symbols using multiple carrier modulation(MCM).

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, amethod of allocating a plurality of data symbols from a transmitting endusing multiple carrier modulation (MCM) includes receiving the pluralityof data symbols from a serial-to-parallel converter, grouping theplurality data symbols into at least one data symbol group, wherein theat least one data symbol group is formed by grouping a specified numberof neighboring data symbols, and allocating the at least one data symbolgroup to at least one subcarrier group, wherein the at least onesubcarrier group is formed by grouping a plurality of subcarriers.

In another aspect of the present invention, a method includes receivingthe plurality of data symbols from a serial-to-parallel converter,precoding the plurality of data symbols by a precoding matrix of the atleast one precoding module, grouping the plurality precoded data symbolsto at least one data symbol group, wherein the at least one data symbolgroup is formed by grouping precoded data symbols that are spaced apartin specified intervals, and allocating the at least one data symbolgroup to at least one subcarrier group, wherein each subcarrier groupcomprises at least one subcarrier and is formed by grouping a pluralityof subcarriers.

In a further aspect of the present invention, a method includesreceiving the plurality of data symbols from a serial-to-parallelconverter, precoding the plurality of data symbols by a precoding matrixof the at least one precoding module, grouping the plurality precodeddata symbols to at least one data symbol group, wherein the at least onedata symbol group is formed by grouping a specified number ofneighboring data symbols, and allocating the at least one data symbolgroup to at least one subcarrier group, wherein each subcarrier groupcomprises at least one subcarrier and is formed by grouping a pluralityof subcarriers.

Yet, in another aspect of the present invention, an apparatus includes asubcarrier-to-symbol mapping modules for receiving the plurality of datasymbols from a serial-to-parallel converter, grouping the plurality datasymbols into at least one data symbol group, wherein the at least onedata symbol group is formed by grouping a specified number ofneighboring data symbols, and allocating the at least one data symbolgroup to at least one subcarrier group, wherein the at least onesubcarrier group is formed by grouping a plurality of subcarriers. Theapparatus further includes a transmitting module for transmitting thedata symbols on the subcarriers of the at least one subcarrier group toa receiving end.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings;

FIG. 1 illustrates a block diagram of transmitting/receiving ends usingan OFDMA scheme in an uplink direction;

FIGS. 2 a-2 c illustrate methods of mapping Nu number of subcarriers outof Nc total number of subcarriers;

FIG. 3 is a block diagram illustrating transmitting/receiving ends usinga DFT spread OFDMA scheme;

FIG. 4 illustrates a subcarrier allocation method according anembodiment of the present invention; and

FIGS. 5 a-5 d illustrate subcarrier allocation methods according toother embodiments of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

Hereinafter, the descriptions of the embodiments will be made withrespect to the OFDMA which is one of many a Multiple Carrier Modulation(MCM) scheme. However, that is merely an exemplary scheme and can beallocated using other types of modulation schemes.

To resolve the ICI problem as well as other problems in the DFT spreadOFDMA system, the following embodiments are provided. As illustrated inFIG. 1, a bit stream of a user (e.g., mobile station) is mapped by aconstellation mapping scheme which is then converted by aserial-to-parallel converter. The descriptions provided hereafter withrespect to the present invention relate to mapping the data symbols tosubcarriers. In the present invention, the processed bit stream is notlimited to a bit stream of a single user but can be multiplexed bitstreams of more than one user (e.g., bit stream of user 1, bit stream ofuser 2, and bit stream of user 3). In addition, although the presentinvention is geared for downlink transmission, the present invention canalso be applied to uplink transmissions.

FIG. 4 illustrates a subcarrier allocation method according anembodiment of the present invention. As illustrated in FIG. 4, a numberof data symbols are grouped into a plurality of groups, and these groupscomprised of data symbols are allocated. More specifically, in order toachieve frequency diversity in an OFDMA system, Nu number of datasymbols are allocated across the entire frequency band having Nc numberof subcarriers when Ns number of neighboring data symbols are formedinto a group, making a total of Ng number of data symbol groups (i.e.,Nu=Ng×Ns). That is, Nu number of data symbols is grouped based onproximity of data symbols (e.g., neighboring data symbols). Usually, thegrouping occurs based on close proximity of the data symbols withrespect to each other. The break up of Nu number of data symbols isbased on Ng number of data symbol groups, which contains Ns number ofelements or data symbols. For example, assuming Nu=12, if four datasymbol groups are formed (Ng=4), then the data symbols that are in closeproximity form a data symbol group of three data symbols (Ns=3). This isdepicted in FIG. 4.

Thereafter, the data symbol groups are allocated to subcarrier groups.Here, each data symbol group is allocated to each subcarrier group,where each subcarrier group comprises a plurality of subcarriers. Inallocating each data symbol group to each subcarrier group, an ICIshould affect only the subcarriers located on the periphery of the datasymbol group so as to express strong characteristics of the ICI.Preferably, the subcarrier groups are offset or spaced apart a certaindistance between neighboring subcarrier groups. Furthermore, it ispreferable to allocate groups by distributing the subcarrier groupsacross the entire frequency band.

FIGS. 5 a-5 d illustrate subcarrier allocation methods according toother embodiments of the present invention. More specifically, theseembodiments illustrate application of the DFT spread OFDMA scheme.

In FIG. 5 a, after being processed by the serial-to-parallel converter,Nu number of data symbols are precoded or spread by a precoding module.Here, the precoding module uses Nu-point DFT scheme. Thereafter, theoutput values (e.g., precoded data symbols) spaced apart at specifiedintervals (e.g., every fourth precoded data symbol) are joined to form adata symbol group. The grouping of precoded data symbols are performeduntil all of the precoded data symbols are placed in data symbol groups.Here, Nu number of precoded data symbols are grouped into Ng number ofdata symbol groups and each data symbol group consists of Ns number ofprecoded data symbols. Subsequently, these data symbol groups areallocated to subcarrier groups whose group formation corresponds to thedata symbol groups. Each subcarrier group is formed by combining acertain number of subcarriers from Nc number of subcarriers. Here, thedata symbols can be transmitted from more than one mobile station.

For example, if Nu=12 and Nc=24 and the DFT output values are {1, 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12}, these output values are grouped into datasymbol groups (e.g., {1, 5, 9}, {2, 6, 10}, {3, 7, 11}, {4, 8, 12})where there are four (4) data symbol groups, Ng=4, and three precodeddata symbols per each group, Ns=3. In this example, the size of Ns isset to 3 data symbols. However, the size of Ns can vary and does nothave to be fixed. In other words, each data symbol group can havedifferent size of Ns. For example, the data groups having differentnumber of data symbols per group can be assembled, such as {1, 4, 9},{2, 10}, {3, 6, 8, 11}, {5, 7, 12}.

Once the formation of the data symbol groups are completed, each datasymbol group (Ng) is allocated to respective subcarrier groups (e.g.,{1, 2, 3}, {7, 8, 9}, {13, 14, 15}, {19, 20, 21} or {4, 5, 6}, {10, 11,12}, {16, 17, 18}, {22, 23, 24}) which are formed by grouping Nc numberof subcarriers. Here, the subcarriers of the subcarriers groups arelocalized. That is, the subcarriers of each subcarrier group areadjacent to each other or put differently, are neighboring subcarriers.However, grouping of subcarriers for the subcarrier group is not limitedto grouping localized or neighboring subcarriers. The subcarrier groupscan group subcarriers that are not close to each other. That is, thesubcarriers of each subcarrier group can have various patterns. As such,non-localized subcarriers or subcarriers that are dispersed can begrouped to form each subcarrier group. (e.g., {1, 9, 17}, {3, 11, 19},{5, 13, 21}, {7, 15, 23}).

In addition, the size of each subcarrier group which corresponds to thesize of the data symbol group does not have to be fixed. As describedabove, each data symbol group size can vary. Accordingly, to correspondwith the varying data symbol group size, the subcarrier group can varyas well. That is, each subcarrier group can be of different size (e.g.,{1, 2}, {6, 7, 8, 9}, {14, 15, 16}, {19, 20, 21, 22}).

By combining the non-localized subcarriers with different subcarriergroup size, it is also possible for the subcarrier group to havedifferent size subcarrier groups, in which the subcarrier groups aredispersed and not localized. For example, the subcarrier groups can be{1, 7}, {4, 9, 15, 24}, {2, 10}, {5, 12, 21}.

As described above, the data symbol groups can have a fixed as well as avarying group size. In addition, the subcarrier groups can also be fixedand/or varying as well. This is true since the size of subcarrier groupscorrespond to the size of the data symbols. Moreover, the subcarriersincluded in the subcarrier groups are either localized subcarriers ornon-localized (dispersed) subcarriers. Here, the detailed description ofthe data symbol groups and the subcarrier groups is not limited to FIG.5 a but can also be applied to the embodiments of FIGS. 5 b-5 d.

In FIG. 5 b, after being processed by the serial-to-parallel converter,Nu number of data symbols are precoded (or spread) by a precodingmodule. Here, the precoding module uses Nu-point DFT scheme. Thereafter,Ns number of neighboring DFT output values are grouped, totaling Ngnumber of data symbol groups. Here, the neighbor DFT output valuesrepresent values that are close each other. Thereafter, the data symbolgroups, consisting of the DFT output values (precoded data symbols), areallocated to subcarriers groups, each of which correspond to each datasymbol group. Each subcarrier group is formed by combining a certainnumber of subcarriers from Nc number of subcarriers and has the samegroup formation as the data symbol group.

For example, if Nu=12 and Nc=24 and the DFT output values (i.e.,precoded data symbols) are {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12},these output values or data symbols are grouped into data symbol groups(e.g., {1, 2, 3}, {4, 5, 6}, {7, 8, 9}, {10, 11, 12}) where there arefour (4) data symbol groups, Ng=4, and three data symbols per group,Ns=3. Once the formation of the data symbol groups are completed, eachdata symbol group is allocated to subcarrier groups (e.g., {1, 2, 3},{7, 8, 9}, {13, 14, 15}, {19, 20, 21} or {4, 5, 6}, {10, 11, 12}, {16,17, 18}, {22, 23, 24}) which are formed by grouping Nc number ofsubcarriers.

In FIG. 5 c, after being processed by the serial-to-parallel converter,Nu number of data symbols are spread (precoded) by Ng number ofprecoding or spreading modules. Here, the precoding module uses Ng-pointDFT spreading scheme. Thereafter, the precoded data symbols areoutputted to different parts of the frequency band. For example, ifthere are four outputted values from a precoding module, each of thesefour outputted data symbols are spread apart so that they are evenlyspaced apart across the frequency band. As illustrated in FIG. 5 c,there are Ng number of precoding modules, and each precoding moduleprocesses Ns number of data symbols. The outputted precoded data symbolsfrom each precoding module are spaced apart in equal intervals.Thereafter, precoded data symbols from each precoding module spacedapart at specified intervals are grouped into data symbol groups towhich subcarriers groups are allocated. Preferably, for example, eachdata symbol group combines only one outputted precoded data symbol fromeach precoding module. Each subcarrier group is formed by combining acertain number of subcarriers from Nc number of subcarriers.

For example, if Nu=12 and Nc=24 and a 4-point DFT output values are, inorder, {1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}, the output valuesare grouped into four data symbol groups (e.g., {1, 5, 9}, {2, 6, 10},{3, 7, 11}, {4, 8, 12}) where Ng=4 having three precoded data symbols ineach data symbol group, Ns=3. Once the formation of the data symbolgroups are completed, each data symbol group is allocated to subcarriergroups (e.g., {1, 2, 3}, {7, 8, 9}, {13, 14, 15}, {19, 20, 21} or {4, 5,6}, {10, 11, 12}, {16, 17, 18}, {22, 23, 24}) which are formed bygrouping Nc number of subcarriers.

In FIG. 5 d, after being processed by the serial-to-parallel converter,Nu number of data symbols are spread by Ng number of precoding modules.Here, the precoding module employs Ns-point DFT scheme. Thereafter, theprecoded data symbols are outputted to different parts of the frequencyband. As illustrated in FIG. 5 d, there are Ng number of precodingmodules, each module processing Ns number of data symbols. Here, Nsnumber of outputted precoded data symbols, considered to be neighboringDFT output values, are grouped, totaling Ng number of data symbolgroups. Here, the neighbor DFT output values represent values that areclose each other. Thereafter, the data symbol groups are allocated tosubcarrier groups. Each subcarrier group is formed by combining acertain number of subcarriers from Nc number of subcarriers.

For example, if Nu=12 and Nc=24 and a 3-point DFT output values are, inorder, {1, 2, 3}, {4, 5, 6}, {7, 8, 9}, {10, 11, 12}, the output valuesare grouped into data symbol groups where Ng=4 and Ns=3. Once theformation of the data symbol groups are completed, each data symbolgroup is allocated to subcarrier groups (e.g., {1, 2, 3}, {7, 8, 9},{13, 14, 15}, {19, 20, 21} or {4, 5, 6}, {10, 11, 12}, {16, 17, 18},{22, 23, 24}) which are formed by grouping Nc number of subcarriers.

In another embodiment of the present invention, an apparatus forallocating the data symbols can be found. The apparatus includes asubcarrier-to-symbol mapping module through which the data symbols aregrouped and mapped to at least one subcarrier group. The apparatusfurther includes a transmitting module for transmitting the data symbolson the subcarriers of the at least one subcarrier group to a receivingend. Since the operations are same as described above with respect toFIGS. 5 a-5 d, further discussions of the operations will be omitted.For details, refers to the descriptions of FIGS. 5 a-5 d.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

The invention claimed is:
 1. A method of allocating a plurality of datasymbols for uplink transmission from a mobile station using OrthogonalFrequency Division Multiple Access (OFDMA), the method comprising:allocating each of the plurality of data symbols to a subcarrier of oneof a plurality of subcarrier groups; and transmitting the allocatedplurality of data symbols to a base station, wherein each of theplurality of subcarrier groups is formed by grouping only a singleplurality of adjacent subcarriers, wherein each of the plurality ofsubcarrier groups is spaced apart a certain distance from neighboringsubcarrier groups such that the plurality of subcarrier groups are notcontiguous in frequency, and wherein at least two consecutive datasymbols of the plurality of data symbols are allocated in sequence to atleast two subcarriers of a subcarrier group of the plurality ofsubcarrier groups in order of increasing subcarrier number in an OFDMsymbol.
 2. The method of claim 1, further comprising: precoding theplurality of data symbols using a precoding matrix.
 3. The method ofclaim 1, wherein each of the plurality of data symbols is associatedwith at least one mobile station (MS).
 4. The method of claim 1, whereinthe single plurality of adjacent subcarriers are orthogonal to eachother.
 5. A method of allocating a plurality of data symbols for uplinktransmission from a mobile station using Orthogonal Frequency DivisionMultiple Access (OFDMA), the method comprising: precoding the pluralityof data symbols using a precoding matrix of at least one precodingmodule; allocating each of the precoded plurality of data symbols to asubcarrier of one of a plurality of subcarrier groups; and transmittingthe allocated plurality of data symbols to a base station, wherein eachof the plurality of subcarrier groups is formed by grouping only asingle plurality of adjacent subcarriers, wherein each of the pluralityof subcarrier groups is spaced apart a certain distance from neighboringsubcarrier groups such that the plurality of subcarrier groups are notcontiguous in frequency, and wherein at least two consecutive datasymbols of the precoded plurality of data symbols are allocated insequence to at least two subcarriers of a subcarrier group of theplurality of subcarrier groups in order of increasing subcarrier numberin an OFDM symbol.
 6. The method of claim 5, wherein the precodingmatrix is a Discrete Fourier Transform (DFT) matrix.
 7. The method ofclaim 5, wherein each of the plurality of subcarrier groups varies insize.
 8. The method of claim 5, wherein each of the plurality ofsubcarrier groups is equivalent in size.
 9. The method of claim 5,wherein the single plurality of adjacent subcarriers are orthogonal toeach other.
 10. An apparatus for allocating a plurality of data symbolsfor uplink transmission using Orthogonal Frequency Division MultipleAccess (OFDMA), the apparatus comprising: a symbol-to-subcarrier mappingmodule, wherein the plurality of data symbols are input to thesymbol-to-subcarrier mapping module and are output from a precodingmodule, wherein, at the symbol-to-subcarrier mapping module, each of theplurality of data symbols is allocated to a subcarrier of one of aplurality of subcarrier groups to transmit the allocated plurality ofdata symbols to a receiving end, wherein each of the plurality ofsubcarrier groups is formed by grouping only a single plurality ofadjacent subcarriers, wherein each of the plurality of subcarrier groupsis spaced apart a certain distance from neighboring subcarrier groupssuch that the plurality of subcarrier groups are not contiguous infrequency, and wherein the symbol-to-subcarrier mapping module isfurther configured to allocate each of the plurality of data symbols byallocating at least two consecutive data symbols of the plurality ofdata symbols in sequence to at least two subcarriers of a subcarriergroup of the plurality of subcarrier groups in order of increasingsubcarrier number in an OFDM symbol.
 11. The apparatus of claim 10,wherein, at the precoding module, the plurality of data symbols areprecoded using a precoding matrix.